It is a trend for IC or semiconductor industries to minimize the size of components. For example, each of multiple chips to be stacked conventionally according to U.S. Pat. No. 5,793,108 must be thinned to a thickness of 2˜4 mils.
Conventional processes for thinning a chip, such as those disclosed in U.S. Pat. Nos. 6,527,627, 6,159,071, include typical steps as shown in FIGS. 1a-1f. In FIG. 1a, tape 3 is stuck onto the front surface 2 (the surface with bonding pad 6 thereon) of wafer 1, so that the back surface 4 of wafer 1 may be ground by grinding machine 30 (as shown in FIG. 1b) to have a thinner wafer 11 (as shown in FIG. 1c). Subsequently a frame 5 to be used in dividing wafer is stuck onto the back surface 14 of thinner wafer 11 (as shown in FIG. 1d), and the tape 3 on the front surface 2 of thinner wafer 11 is removed thereafter (as shown in FIG. 1e) so that thinner wafer 11 can be divided (or diced) by sawing machine 40 (as shown in FIG. 1f).
Thinner wafer 11, obtained by grinding according to the conventional processes as described above, is always subjected to warpage (as shown in FIG. 2) due to stress residue resulting from grinding, bringing difficulty and trouble for subsequent steps, leading to vulnerability to crack of thinner wafer 11. Furthermore, the chip or die 21 (as shown in FIG. 3) obtained from dividing thinner wafer 11, being so thin, always tends to be subjected to crack 8 when picked up (e.g. picked up by a pick-up head 50 as shown in FIG. 3) during the process of Die Bond in which the chip (or die) 21 is moved to substrate (as shown in FIG. 4). The chip (or die) 21 is also subjected to crack 8 even when it is placed on substrate 7 (also can be seen from FIG. 4).
In order to solve the poor quality problem resulting from thinner wafer, U.S. Pat. No. 6,264,535 disclosed a technology as shown in FIGS. 5a-5e. Referring to FIGS. 5a-5e (based on the technology according to U.S. Pat. No. 6,264,535), after front surface 2 of wafer 1 is sawn (by sawing machine 40) to have recesses 9 (not sawn to bottom), tape 3 is stuck onto front surface 2, and back surface 4 of wafer 1 is ground by grinding machine 30, thereby a group of separated dice 21 are obtained, and frame 12 is then stuck onto back surface 4 of dice 21, subsequently tape 3 is removed from the front surface of the dice 21. Although the process according to U.S. Pat. No. 6,264,535 may likely more or less ease the problem of wafer crack resulting from thinning a wafer, it is subject to much complication (e.g. plural times of sticking tape and frame, etc), and incurs higher cost, not to mention that it is not for solving the problem of crack of thinner die inherent in the die bonding process thereafter. Further reference is made now with respect to JP patent 2003059871 which is for solving similar problem.
According to JP patent 2003059871, a reinforced thin film is stuck to the tape used in grinding a wafer, and the thin film is reinforced by a support layer made of thermo-softening resin with specific storage elasticity. Although the reinforced structure according to JP patent 2003059871 might more or less provide some usefulness in resolving the problem, it requires using specific material, resulting in higher cost and more complication. Still further reference is made now with respect to JP patent 11265928 which is for solving similar problem. According to JP patent 11265928, a wafer to be polished is stuck onto a surface of a specific plate, where the coarseness of the surface is controlled to be in a specific range. The technology according to JP patent 11265928, even if useful, to some extent, for solving the problem inherent in thinning a wafer, is not necessarily helpful to the reduction of process difficulty and product failure rate in the steps following the process of thinning a wafer.
In view of the fact no ideal solution has ever come up, the present invention not only develops a process for related industries to eliminate or reduce negative effect and/or product failure rate resulting from thinning (e.g. grinding) and/or dividing a wafer, but also provides efficacy of simplification and benefit of lowering cost for the process following thinning and/or dividing a wafer.
Difference Between the Present Invention and Prior Arts
One of the main features of the present invention is the dividing step in which a semiconductor (such as a wafer) with transparent material thereon is divided, by taking advantage of transparency of the transparent material, into dice each with the transparent material thereon. The dividing step includes: cutting the transparent material (64 in FIG. 6f of the present application) which is on the active surface (61 in FIG. 6f of the present application) of the wafer, to reach the active surface of the wafer, and cutting the wafer from the active surface to obtain at least a die which has transparent material remaining on its active surface (67 in FIG. 6f of the present application). For example, the transparent material is cut according to a division line on the active surface of the wafer, so that the division line is reached after the transparent material is cut, and the wafer is then cut according to the division line or from the division line to obtain a die. It is by the transparency of transparent material that the wafer with transparent material on its active surface can be cut into dice each with transparent material remaining on the active surface thereof. The dividing step is done after thinning the wafer which has had the transparent material stuck on the active surface thereof.
No prior arts have ever been known which has the same feature as or similar feature to the dividing step of the present invention. Some prior arts are cited as follows to highlight the unique feature of the present invention. All the reference figures and reference numbers mentioned below in regard to these prior arts are not shown in the present application, but shown in their U.S. patent application/Issue Publication.
According to US Patent Application 20070015342 (specifically FIGS. 16-18 thereof), protective tape 2 (FIG. 16 thereof) on the active surface of a wafer is peeled off before cutting the wafer into dice (FIG. 18 thereof). The dividing step according to US Patent Application 20070015342 includes: peeling off the protective tape 2 (FIG. 16 thereof) from the active surface of a wafer, and cutting the wafer from the active surface to obtain dice. In contrast, according to the present invention, the transparent material (64 in FIG. 6f of the present application) on the active surface (61 in FIG. 6f of the present application) of a wafer, together with the wafer, are cut into dice (66 in FIG. 6f of the present application) each with part of the transparent material remaining on the active surface thereof, i.e., the dividing step according to the present invention includes: first cutting (instead of peeling off) the transparent material on the active surface of a wafer, to reach the active surface (specifically, to reach a division line on the active surface) of the wafer, and then cutting the wafer from the active surface (specifically, from the division line on the active surface) to obtain at least a die (66 in FIGS. 6f-6g of the present application). After the dividing step according to the present invention, the transparent material remains on the active surface of the obtained die, providing convenience for processing the obtained die. For example, the transparent material remaining on the obtained die can significantly reduce the chance that the obtained die is hurt when moving it to a carrier.
It is obvious now that there can be no protective tape on the active surface of each die obtained from dividing a wafer into dice according to US Patent Application 20070015342, and each die (specifically the active surface thereof) has no material (such as the transparent material according to the present invention) for its protection when it is processed (e.g. when the obtained die is moved to a wiring substrate 91 as shown in FIG. 20 of the US publication of the prior art). The significant difference between the present invention and US Patent Application 20070015342, results from the fact that the present invention makes use of transparency of the transparent material stuck on the active surface of a wafer, thereby the wafer can be cut into dice without need of taking off the transparent material beforehand. In contrast, prior art US Patent Application 20070015342 has to peel off protective tape from a wafer before cutting the wafer into dice.
According to US Patent Application 20070179127 (specifically FIGS. 3A-3F thereof), after grinding a wafer from its inactive surface to reach the bottom of grooves 33, the wafer has been divided into dice each adhering to adhesive layer 23 which adheres to protection tape 34, each of the dice is then moved up to separate it from the protection tape 34, and adhesive layer 23 is torn off and cut off. In contrast, according to the present invention, after the process of grinding a wafer, the transparent material on the active surface of the wafer is cut to reach the active surface (specifically to reach a division line on the active surface), and then the wafer is cut from its active surface (specifically from a division line on the active surface) to obtain dice, i.e., the dividing step according to the present invention includes: first cutting the transparent material (64 in FIG. 6f of the present application) which is on the active surface (61 in FIG. 6f of the present application) of a wafer, to reach the active surface (specifically to reach a division line on the active surface) of the wafer, and then cutting the wafer from the active surface (specifically from the division line on the active surface) to obtain dice (66 in FIGS. 6f-6g of the present application). The contrast stated above results in the fact that the die obtained from cutting a wafer according to the present invention has transparent material remaining between the active surface thereof and an open space, while the die obtained from cutting a wafer according to the prior art (US Patent Application 20070179127) has adhesive layer and/or protection tape remaining between the active surface thereof and a backholder 36. One feature (transparent material remaining between an open space and the active surface of a die obtained from cutting a wafer) of the present invention provides benefit for processing the die (e.g. for minimizing the chance of hurting the die when moving it to a carrier). The benefit provided by the present invention originates from using transparent material and making use of transparency of the transparent material, which is unique in contrast with known prior arts.
According to U.S. Pat. No. 6,264,535 (admitted prior art shown by FIGS. 5a-5e of the present application), after grinding a wafer 1 from its inactive surface 4, the wafer 1 has been divided into dice 21 with active surface adhering to tape 3, the tape 3 is then peeled off to obtain dice each separated from another as shown in FIG. 5e of the present invention. In contrast, according to the present invention, after grinding a wafer, the transparent material (64 in FIG. 6f of the present application) on the active surface (61 in FIG. 6f of the present application) of a wafer, together with the wafer, are cut into dice (66 in FIG. 6f of the present application) each with part of the transparent material remaining on the active surface thereof and separate from another part (the part of transparent material which is on the active surface of another one of the dice), i.e., the dividing step according to the present invention includes: first cutting the transparent material on the active surface of a wafer, to reach the active surface (specifically, to reach a division line on the active surface) of the wafer, and then cutting the wafer from the active surface (specifically, from the division line on the active surface) to obtain dice (66 in FIGS. 6f-6g of the present application). After cutting a wafer into dice according to the present invention, each die is adhered by one part of transparent material which is on its active surface and is separated from another die, thereby each of the dice can be processed separately and with minimized chance of getting hurt. For example, each of the dice can be moved separately to a carrier with minimized chance of getting hurt.
At least one of the main features of the present invention, which results from using transparent material and making use of transparency of the transparent material, is unique as can be seen from foregoing explanations. Not only one but also the other features of the present invention shall be deemed unique in contrast to prior arts, as will be seen from the following descriptions.